1. Field of the Invention
The present invention relates to a diesel engine, particularly a diesel engine piston that greatly increases combustion efficiency by minimizing spray overlap in dual spraying of fuels.
2. Description of Related Art
In general, it is the most important to improve combustion in a diesel engine that ignites and burns fuel by spraying the fuel into a compressed air at a predetermined temperature or more in order to reduce noxious exhaust gas and prevent deterioration of fuel efficiency.
Accordingly, the combustion chamber formed in a piston is shaped such that flow improving mix of air and fuel is formed and fuel atomization is promoted.
The flow means swirl, vortex, or tumble.
The fuel atomization means a technology for increasing a mixing performance with the atmosphere air by allowing a fuel sprayed from an injector to be composed of groups of droplets including many small droplets to increase the surface areas of the droplets.
The promotion of atomization may be implemented by the physical shape of the injector nozzle, interaction with the air hitting in spraying, or hitting against the wall of the combustion chamber, and the structure of the combustion chamber is determined in consideration of further improving this phenomenon.
In general, when at least two or more fuels are simultaneously sprayed into the combustion chamber from the injector, possibility of overlap of the spray fuels in the combustion chamber may increase, such that the risk of incomplete combustion correspondingly increases.
Actually, the incomplete combustion caused by overlap of the spray fuels is necessarily considered in design of the combustion chamber because it reduces the fuel efficiency of the engine and generates a large amount of noxious exhaust gas.
FIG. 5 shows a partial configuration of a piston having a combustion chamber for promoting flow and fuel atomization.
As shown in the figure, a combustion chamber 52 is a combustion space recessed at a predetermined depth from the top 53 of a piston body 50, the cross-sectional shape of the combustion space is specified by a profile surface 55 forming the inner wall of the combustion space, and the combustion space is made symmetric by a pip 59 protruding into the combustion space from the bottom of the combustion space.
Profile surface 55 forming the inner wall of the combustion space is an important factor that promotes flow and fuel atomization in the combustion space, in the structure of combustion chamber 52.
For this configuration, profile surface 55 forms a protrusion 57 that protrudes inward the combustion space, such that the fuel sprayed from the injector hits against the wall of the combustion chamber and atomization is promoted.
Profile surface 55 forms a bowl rim 58 having an arc shape under protrusion 57 and forms an inclined portion 56 connected to top 53 at an angle above bowl rim 58, such that flow required for the combustion chamber is formed.
The pip 59 inclines at a predetermined angle aa from the center in a substantially conical shape.
Combustion chamber 52 promotes flow and fuel atomization in the combustion space while profile surface 55 and pip 59 are optimally designed with respect to the entire depth Ha of combustion chamber 52 to improve fuel efficiency.
The optimum design is that, for example, for pip 59 protruding into the combustion space, the protrusion height ha is set at a specific ratio to the entire depth Ha of combustion chamber 52, and a formation height Laa of bowl rim 58 of profile surface 55 forming the inner wall of the combustion space, a connection height Lbb of protrusion 57, and an extension height Lcc of inclined portion 56 are set at a specific ratio to the entire depth Ha of combustion chamber 52.
The height Laa+Lbb to protrusion 57 starting to be inclined to form inclined portion 56 at bowl rim 58 is a critical height Taa, which means a set value for more effectively collecting fuel hitting against protrusion 57 to bowl rim 58 where flow is formed.
However, when combustion chamber 52 has the structure described above, flow and fuel atomization in the combustion space is considerably improved, but the risk for overlap of at least two or more fuels sprayed from the injector is still high.
FIGS. 6A and 6B show a spray overlap phenomenon that occurs in duel spraying of fuels in combustion chamber 52 shown in FIG. 5.
As shown in FIG. 6A, first and second spray fuels 310 and 320 that are sprayed into combustion chamber 52 from an injector are divided at predetermined angles and hit against profile surface 55, but as shown in FIG. 6B, first and second spray fuels 310 and 320 have the same spray angles (generally, 152 degrees), such the dispersion areas overlap when the fuels hit against protrusion 57 of profile surface 55.
Therefore, an overlap area Iab is generated between an atomization area Ia where first spray fuel 310 hits against a portion of protrusion 57 and another atomization Ib area where second spray fuel 320 hits against another portion of protrusion 57.
The more the number of spray fuels sprayed into combustion chamber 52 from the injector, the larger the overlap area Iab.
The overlap of the spray fuels causes incomplete combustion and the incomplete combustion further decreases fuel efficiency of the engine and increases the amount of noxious exhaust gas, which has a limit in following the vehicle regulation that becomes restrict(tightened?).
Korean Patent Application Laid-Open No. 10-2009-0025655 (Mar. 11, 2009) relates to an combustion chamber structure of a diesel engine having a variable compression ratio (see FIG. 1, and paragraph Nos. 16 to 18 in Page 3).
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.